In order to ensure perfect functioning of electronical devices, it is important to protect them from overload, i.e. from too high through-currents. A frequent consequence of overload is heating of the electronical device. Using a temperature sensor mounted to the electronical device, overload of the electronical device can be determined. A multi-chip solution including overload protection is described in EP 0208970 A1 and U.S. Pat. No. 4,937,646 and is shown in FIG. 7. In this example, the temperature sensor has been mounted in the form of a thyristor 710 on a field-effect transistor (MOSFET) 720 which in turn is located on a leadframe 730 and comprises a source terminal (S), a gate terminal (G) and a drain terminal (D) (not shown). The thyristor is dimensioned such that it switches on before a critical temperature for the MOSFET of 150 to 180° C. is reached. Thus, the gate source capacitance of the MOSFET is short-circuited and the MOSFET switches off.
Further development in the integration in power transistor technologies has resulted in the current density increasing strongly. This increase can take place in a very short time and the result in an overload case will be very large temperature gradients. Detecting the temperature by a separate chip is delayed due to thermal capacitances and this delay may result in the power transistor not to be protected in time and the power transistor to be destroyed.